Non-oriented electrical steel sheet having an excellent high-frequency iron loss property

ABSTRACT

A non-oriented electrical steel sheet has a chemical composition that includes C: not more than 0.005%, Si: 1.5-4%, Mn: 1.0-5%, P: not more than 0.1%, S: not more than 0.005%, Al: not more than 3 mass %, N: not more than 0.005 mass %, Bi: not more than 0.0030% as mass % and the remainder being Fe and inevitable impurities or a chemical composition containing C: not more than 0.005%, Si: 1.5-4%, Mn: 1.0-5%, P: not more than 0.1%, S: not more than 0.005%, Al: not more than 3 mass %, N: not more than 0.005 mass %, Bi: not more than 0.0030% and further one or two of Ca: 0.0005-0.005% and Mg: 0.0002-0.005%, and is stably excellent in the high-frequency iron loss property even if a great amount of Mn is included.

TECHNICAL FIELD

This disclosure relates to a non-oriented electrical steel sheet havingan excellent high-frequency iron loss property.

BACKGROUND

A motor for a hybrid car or an electric car is driven at a highfrequency region of 400-2 kHz from a viewpoint of miniaturization andhigh efficiency. A non-oriented electrical steel sheet used in a corematerial for such a high-frequency motor is desired to be low in ironloss at a high frequency.

It is effective to decrease sheet thickness and increase specificresistance to reduce the iron loss at a high frequency. In the method ofdecreasing the sheet thickness, however, not only handling becomesdifficult due to a decrease in rigidity in the materials, but also thenumber of punching steps or lamination steps is increased, so that thereis a problem of deteriorating productivity. On the contrary, the methodof increasing the specific resistance does not have the abovedisadvantage, so that it can be said to be desirable as a method ofreducing high-frequency iron loss.

Addition of Si is effective to increase the specific resistance.However, Si is an element having a large solid-solution strengtheningability so that there is a problem that the material is hardened withthe increase in the amount of Si to deteriorate the rolling property. Asone means to solve the above problem, there is a method of adding Mninstead of Si. Since Mn is small in its solid-solution strengtheningability compared to Si, the high-frequency iron loss can be reducedwhile suppressing deterioration of productivity.

As a technique of utilizing the above effect by Mn addition, forexample, JP 2002-47542 A discloses a non-oriented electrical steel sheetcontaining Si: 0.5-2.5 mass %, Mn: 1.0-3.5 mass % and Al: 1.0-3.0 mass%. Also, JP 2002-30397 A discloses a non-oriented electrical steel sheetcontaining Si: not more than 3.0 mass %, Mn: 1.0-4.0 mass % and Al:1.0-3.0 mass %.

However, the techniques disclosed in JP 2002-47542 A and JP 2002-30397 Ahave a problem that hysteresis loss is increased with the increase of Mnaddition amount and, hence, the desired effect of reducing iron loss maynot be obtained.

It could therefore be helpful to provide a non-oriented electrical steelsheet having a stable and excellent high-frequency iron loss propertyeven if a great amount of Mn is contained.

SUMMARY

We found that the deterioration of high-frequency iron loss property inhigh Mn-added steels is based on the presence of Bi included as animpurity and, hence, the high frequency iron loss can be reduced stablyby suppressing the Bi content even at a high Mn content.

We thus provide a non-oriented electrical steel sheet having a chemicalcomposition comprising C: not more than 0.005 mass %, Si: 1.5-4 mass %,Mn: 1.0-5 mass %, P: not more than 0.1 mass %, S: not more than 0.005mass %, Al: not more than 3 mass %, N: not more than 0.005 mass %, Bi:not more than 0.0030 mass % and the remainder being Fe and inevitableimpurities.

The non-oriented electrical steel sheet may contain one or two of Ca:0.0005-0.005 mass % and Mg: 0.0002-0.005 mass % in addition to the abovechemical composition.

Also, the non-oriented electrical steel sheet may further contain one ortwo of Sb: 0.0005-0.05 mass % and Sn: 0.0005-0.05 mass % in addition tothe above chemical composition.

Further, the non-oriented electrical steel sheet may further contain Mo:0.0005-0.0030 mass % in addition to the above chemical composition.

Moreover, the non-oriented electrical steel sheet may still furthercontain Ti: not more than 0.002 mass %.

It is thus possible to produce a non-oriented electrical steel sheethaving an excellent high-frequency iron loss property stably bysuppressing the content of Bi included as an impurity even with a highMn addition amount.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the influence of Bi content upon therelationship between Mn content and high-frequency iron loss W_(10/400).

FIG. 2 is a graph showing the relationship between Bi content andhigh-frequency iron loss W_(10/400).

DETAILED DESCRIPTION

Experiments concerning our steel sheets and methods will first bedescribed.

A steel containing C: 0.0016 mass %, Si: 3.35 mass %, P: 0.013 mass %,S: 0.0004 mass %, Al: 1.4 mass % and N: 0.0018 mass % and added with Mnchanged within a range of 0.1-5.2 mass % is melted in a laboratory toform a steel ingot, which is hot rolled, subjected to a hot bandannealing at 1000° C. in an atmosphere of 100 vol % N₂ for 30 seconds,cold rolled to a cold rolled sheet of 0.30 mm in thickness and subjectedto a final annealing at 1000° C. in an atmosphere of 20 vol % H₂-80 vol% N₂ for 30 seconds.

In FIG. 1, symbol  shows the above experimental results as therelationship between Mn addition amount and iron loss W_(10/400). Asseen from these results, when Mn is less than 1 mass %, the iron loss isdecreased with the increase in Mn addition amount, but the decrease ofthe iron loss becomes gentle at an amount of not less than 1 mass % and,rather, the iron loss is increased at an amount exceeding 4 mass %. Whenthe steel sheet containing 2 mass % of Mn is observed by TEM, granularBi is found in grain boundaries.

To further investigate the influence of Bi upon the magnetic properties,a steel prepared by adding Mn variously changed within a range of0.1-5.2 mass % to a high-purity steel containing C: 0.0014 mass %, Si:3.33 mass %, Al: 1.2 mass %, P: 0.014 mass %, S: 0.0006 mass %, N:0.0020 mass % and Bi: not more than 0.0010 mass % is melted in alaboratory and shaped into a cold rolled and annealed sheet in the samemanner as in the above experiment to measure an iron loss W_(10/400).

The thus obtained experimental results are shown by symbol ▴ in FIG. 1.As seen from these results, the iron loss is reduced with the increasein the Mn addition amount in the cold rolled and annealed sheet madefrom a high-purity steel having a decreased Bi content as compared tothe steel sheet shown by symbol . When the steel sheet containing 2mass % of Mn is observed by TEM, granular Bi is not found in the grainboundaries. From this fact, we believe that the increase of the ironloss associated with the increase of Mn addition amount in the steelsheet of symbol  is based on the increase of hysteresis loss due tofine precipitation of Bi.

In the steel sheet containing less than 1 mass % of Mn, the effect ofimproving the iron loss by the decrease in Bi is found, but the ratiothereof is small. Although the reason is not clear sufficiently, webelieve that the driving force for grain growth is lowered by solutedrag of Mn in the steels having an increased Mn amount and, hence, thegrain growth is easily and largely influenced by the presence of fineBi.

In general, Bi is an impurity incorporated from scrap so that not onlythe amount incorporated, but also the deviation thereof becomesgradually large associated with the increased use of scrap in recentyears. Such an increase of Bi content is not a big problem in electricalsteel sheets having a low Mn content, but the steels having a high Mncontent are largely influenced by a slight amount of Bi because thegrain growth is lowered by solute drag of Mn.

To investigate the influence of Bi content on the iron loss, a steelprepared by adding Bi variously changed within a range of tr. to 0.0045mass % to a steel containing C: 0.0022 mass %, Si: 3.20 mass %, Mn: 1.7mass %, Al: 1.3 mass %, P: 0.014 mass %, S: 0.0005 mass % and N: 0.0020mass % is melted in a laboratory and shaped into a cold rolled andannealed sheet of 0.30 mm in thickness in the same manner as in theabove experiment to measure an iron loss W_(10/400).

FIG. 2 shows the above experimental results as the relationship betweenBi content and iron loss W_(10/400). As seen from FIG. 2, the iron losslargely decreases when the Bi content is not more than 0.0030 mass %(not more than 30 massppm). This is due to the fact that the graingrowth is improved by decreasing Bi. From this fact, we confirmed thatthe Bi content needs to be decreased to not more than 0.0030 mass % tosuppress the bad influence of Bi upon grain growth.

There will be described the chemical composition in the non-orientedelectrical steel sheet.

C: Not More than 0.005 mass %

C is an element forming a carbide with Mn. When it exceeds 0.005 mass %,the amount of Mn-based carbide is increased to block the grain growth,so that an upper limit is 0.005 mass %. Preferably, it is not more than0.002 mass %.

Si: 1.5-4 mass %

Si is an element effective to increase the specific resistance of steeland reducing iron loss and is added in an amount of not less than 1.5mass %. While when it is added in an amount exceeding 4 mass %, themagnetic flux density is lowered, so that an upper limit is 4 mass %.Preferably, the lower limit of Si is 2.0 mass % and the upper limitthereof is 3.0 mass %.

Mn: 1.0-5 mass %

Mn is effective in increasing the specific resistance of steel andreducing an iron loss without largely damaging the workability and is animportant ingredient added in an amount of not less than 1.0 mass %. Tofurther obtain the effect of reducing iron loss, it is preferable to beadded in an amount of not less than 1.6 mass %. While when it is addedin an amount exceeding 5 mass %, the magnetic flux density is lowered,so that an upper limit is 5 mass %. Preferably, the lower limit of Mn is2 mass % and the upper limit thereof is 3 mass %.

P: Not More than 0.1 mass %

P is an element having a large solid-solution strengthening ability, butwhen it is added in an amount exceeding 0.1 mass %, the steel sheet issignificantly hardened to deteriorate productivity, so that it islimited to not more than 0.1 mass %. Preferably, it is not more than0.05 mass %.

S: Not More than 0.005 mass %

S is an inevitable impurity. When it is included in an amount exceeding0.005 mass %, MnS is precipitated to block the grain growth and increaseiron loss, so that an upper limit is 0.005 mass %. Preferably, it is notmore than 0.001 mass %.

Al: Not More than 3 mass %

Al is an element effective to increase the specific resistance of steeland reducing iron loss like Si. When it is added in an amount exceeding3 mass %, the magnetic flux density is lowered, so that an upper limitis 3 mass %. Preferably, it is not more than 2 mass %. However, when Alcontent is less than 0.1 mass %, fine AN is precipitated to block graingrowth and increase iron loss, so that a lower limit is preferable to be0.1 mass %.

N: Not More than 0.005 mass %

N is an inevitable impurity penetrated from ambient air into steel. Whenthe content is large, grain growth is blocked due to the precipitationof AlN to increase the iron loss, so that an upper limit is restrictedto 0.005 mass %. Preferably, it is not more than 0.003 mass %.

Bi: Not More than 0.0030 mass %

Bi is an important element to be controlled because it badly affects thehigh-frequency iron loss property. When Bi content exceeds 0.0030 mass %as seen from FIG. 2, the iron loss violently increases. Therefore, Bi isrestricted to not more than 0.0030 mass %. Preferably, it is not morethan 0.0010 mass %.

The non-oriented electrical steel sheet preferably contains one or twoof Ca and Mg in addition to the above chemical composition.

Ca: 0.0005-0.005 mass %

Ca is an element effective in forming a sulfide and coarsening bycompositely precipitating with Bi to suppress the adverse effect of Biand reduce iron loss. It is preferable to be added in an amount of notless than 0.0005 mass % to obtain such an effect. However, when it isadded in an amount exceeding 0.005 mass %, the amount of CaSprecipitated becomes too large and iron loss is adversely increased, sothat an upper limit is preferable to be 0.005 mass %. More preferably,the lower limit of Ca is 0.001 mass % and the upper limit thereof is0.004 mass %.

Mg: 0.0002-0.005 mass %

Mg is an element effective in forming an oxide and coarsening bycompositely precipitating with Bi to suppress the adverse effect of Biand reduce iron loss. It is preferable to be added in an amount of notless than 0.0002 mass % to obtain such an effect. However, additionexceeding 0.005 mass % is difficult and brings about an increase incost, so that an upper limit is preferable to be 0.005 mass %. Morepreferably, the lower limit of Mg is 0.001 mass % and the upper limitthereof is 0.004 mass %.

Also, the non-oriented electrical steel sheet preferably furthercontains the following ingredients in addition to the above chemicalcomposition.

Sb: 0.0005-0.05 mass %, Sn: 0.0005-0.05 mass %

Sb and Sn have an effect of improving the texture to increase themagnetic flux density, so that they can be added in an amount of notless than 0.0005 mass % alone or in admixture. More preferably, it isnot less than 0.01 mass %. However, addition exceeding 0.05 mass %brings about embrittlement of the steel sheet, so that an upper limit ispreferable to be 0.05 mass %. More preferably, the lower limit of eachof Sb and Sn is 0.01 mass % and the upper limit thereof is 0.04 mass %.

Mo: 0.0005-0.0030 mass %

Mo has an effect of coarsening the resulting carbide to reduce iron lossand is preferably added in an amount of not less than 0.0005 mass %.However, when it is added in an amount exceeding 0.0030 mass %, theamount of the carbide becomes too large and the iron loss is ratherincreased, so that an upper limit is preferable to be 0.0030 mass %.More preferably, the lower limit of Mo is 0.0010 mass % and the upperlimit thereof is 0.0020 mass %.

Ti: Not More than 0.002 mass %

Ti is an element forming a carbonitride. When the content is large, theamount of the carbonitride precipitated becomes too large, so that thegrain growth is blocked and the iron loss is increased. Therefore, Ti ispreferably restricted to not more than 0.002 mass %. More preferably, itis not more than 0.001 mass %.

In the non-oriented electrical steel sheet, the remainder other than theaforementioned ingredients is Fe and inevitable impurities. However,other elements may be included within a range not damaging the desiredeffect.

Next, our production method of our non-oriented electrical steel sheetwill be described below.

In the method of producing the non-oriented electrical steel sheet,conditions are not particularly limited except that the chemicalcomposition of the steel sheet is controlled within our defined range,so that production may be performed under the same conditions as in thenormal non-oriented electrical steel sheet. For example, the steel sheetcan be produced by a method wherein a steel having a chemicalcomposition is melted, for example, in a converter, a degassing deviceor the like and shaped into a raw steel material (slab) by a continuouscasting method or an ingot making-blooming method, which is hot rolled,subjected to a hot band annealing as required and further to a singlecold rolling or two or more cold rollings including an intermediateannealing therebetween to a predetermined sheet thickness andsubsequently to a final annealing.

EXAMPLES

A steel having a chemical composition shown in Table 1 is melted in aconverter, degassed by blowing and continuously cast into a slab, whichis heated at 1100° C. for 1 hour, hot rolled at a final rollingtemperature of 800° C. and wound into a coil at a temperature of 610° C.to obtain a hot rolled sheet of 1.8 mm in thickness. Thereafter, the hotrolled sheet is subjected to a hot band annealing at 1000° C. in anatmosphere of 100 vol % N₂ for 30 seconds and cold rolled to obtain acold rolled sheet having a sheet thickness of 0.35 mm, which issubjected to a final annealing at 980° C. in an atmosphere of 20 vol %H₂-80 vol % N₂ for 15 seconds to form a cold rolled and annealed sheet.

From the thus cold rolled and annealed sheet are cut out Epstein sampleswith a width: 30 mm×a length: 280 mm in the rolling direction and in adirection perpendicular to the rolling direction to measure an iron lossW_(10/400) and a magnetic flux density B₅₀ according to JIS C2550,respectively. These results are shown in Table 1.

TABLE 1 Chemical composition (mass %) No C Si Mn P S Al N Bi Ca Mg Sb  10.0015 3.20 1.59 0.011 0.0003 1.20 0.0020 0.0002 tr. tr. tr.  2 0.00123.12 1.59 0.011 0.0004 1.20 0.0015 0.0011 tr. tr. tr.  3 0.0013 3.131.57 0.011 0.0003 1.16 0.0016 0.0020 tr. tr. tr.  4 0.0015 3.14 1.560.011 0.0002 1.16 0.0016 0.0027 tr. tr. tr.  5 0.0017 3.21 1.60 0.0120.0003 1.15 0.0014 0.0037 tr. tr. tr.  6 0.0017 3.15 1.59 0.013 0.00041.18 0.0015 0.0045 tr. tr. tr.  7 0.0016 3.16 0.15 0.012 0.0003 1.170.0014 0.0002 tr. tr. tr.  8 0.0000 3.14 0.91 0.011 0.0003 1.16 0.00150.0001 tr. tr. tr.  9 0.0019 3.16 1.55 0.012 0.0004 1.16 0.0013 0.0003tr. tr. tr. 10 0.0022 3.22 2.51 0.013 0.0003 1.15 0.0014 0.0002 tr. tr.tr. 11 0.0016 3.16 3.49 0.012 0.0003 1.18 0.0017 0.0003 tr. tr. tr. 120.0014 3.15 4.43 0.014 0.0004 1.18 0.0016 0.0004 tr. tr. tr. 13 0.00143.16 5.20 0.010 0.0004 1.17 0.0023 0.0003 tr. tr. tr. 14 0.0014 3.140.50 0.013 0.0005 1.20 0.0019 0.0025 tr. tr. tr. 15 0.0013 3.15 1.530.012 0.0003 1.17 0.0017 0.0005 tr. tr. tr. 16 0.0017 3.17 1.52 0.0130.0003 1.18 0.0019 0.0003 tr. tr. 0.0053 17 0.0011 3.16 1.57 0.0110.0004 1.20 0.0018 0.0003 tr. tr. 0.0174 18 0.0014 3.14 1.56 0.0120.0003 1.20 0.0016 0.0005 tr. tr. tr. 19 0.0016 3.20 1.56 0.012 0.00041.16 0.0021 0.0004 tr. tr. tr. 20 0.0018 3.14 1.56 0.014 0.0004 1.210.0019 0.0003 tr. tr. tr. 21 0.0021 3.12 1.57 0.013 0.0003 1.20 0.00170.0005 0.0023 tr. tr. 22 0.0020 3.17 1.55 0.012 0.0004 1.21 0.00160.0015 0.0035 tr. tr. 23 0.0021 3.13 1.56 0.012 0.0005 1.20 0.00170.0015 0.0047 tr. tr. 24 0.0016 3.14 1.54 0.013 0.0003 1.22 0.00180.0016 0.0060 tr. tr. 25 0.0017 3.13 1.54 0.011 0.0003 1.21 0.00160.0035 0.0032 tr. tr. 26 0.0015 3.18 1.53 0.012 0.0004 1.23 0.00150.0005 tr. 0.0014 tr. 27 0.0016 3.19 1.54 0.011 0.0004 1.24 0.00210.0015 tr. 0.0015 tr. 28 0.0014 3.22 1.57 0.012 0.0003 1.22 0.00200.0015 tr. 0.0041 tr. 29 0.0013 0.88 1.52 0.030 0.0004 2.60 0.00250.0003 tr. tr. tr. 30 0.0015 3.14 1.53 0.012 0.0003 1.22 0.0017 0.0002tr. tr. tr. 31 0.0017 3.16 1.54 0.012 0.0003 1.23 0.0016 0.0003 tr. tr.tr. 32 0.0016 3.18 1.56 0.012 0.0004 1.20 0.0017 0.0002 tr. tr. tr. 330.0014 2.22 1.26 0.012 0.0003 2.18 0.0021 0.0005 tr. tr. tr. 34 0.00163.55 1.20 0.004 0.0004 1.14 0.0021 0.0003 tr. tr. tr. 35 0.0017 4.921.13 0.004 0.0003 0.32 0.0016 0.0003 tr. tr. tr. 36 0.0015 2.79 1.580.013 0.0003 1.33 0.0017 0.0005 tr. tr. tr. 37 0.0014 2.49 1.57 0.0110.0004 2.44 0.0021 0.0005 tr. tr. tr. 38 0.0018 1.52 1.58 0.012 0.00043.47 0.0022 0.0002 tr. tr. tr. 39 0.0013 2.79 1.56 0.013 0.0017 1.320.0014 0.0003 tr. tr. tr. 40 0.0015 2.79 1.57 0.011 0.0055 1.32 0.00160.0002 tr. tr. tr. 41 0.0016 2.78 1.58 0.014 0.0004 1.33 0.0015 0.0003tr. tr. tr. 42 0.0017 2.79 1.56 0.013 0.0003 1.32 0.0060 0.0005 tr. tr.tr. 43 0.0059 2.79 1.57 0.012 0.0005 1.32 0.0010 0.0002 tr. tr. tr.Magnetic properties Magnetic Chemical composition Sheet Iron loss flux(mass %) thickness W_(10/400) density No Sn Mo Ti (mm) (W/kg) B₅₀ (T)Remarks  1 tr. 0.0013 0.0002 0.35 15.20 1.67 Invention Steel  2 tr.0.0008 0.0001 0.35 15.21 1.67 Invention Steel  3 tr. 0.0014 0.0002 0.3515.28 1.67 Invention Steel  4 tr. 0.0015 0.0001 0.35 15.30 1.67Invention Steel  5 tr. 0.0010 0.0002 0.35 15.76 1.68 Comparative Steel 6 tr. 0.0011 0.0002 0.35 16.11 1.68 Comparative Steel  7 tr. 0.00110.0003 0.35 16.00 1.69 Comparative Steel  8 tr. 0.0014 0.0002 0.35 15.701.68 Comparative Steel  9 tr. 0.0012 0.0001 0.35 15.30 1.68 InventionSteel 10 tr. 0.0010 0.0002 0.35 15.10 1.66 Invention Steel 11 tr. 0.00140.0002 0.35 15.04 1.65 Invention Steel 12 tr. 0.0013 0.0002 0.35 15.001.65 Invention Steel 13 tr. 0.0013 0.0002 0.35 15.02 1.61 ComparativeSteel 14 tr. 0.0009 0.0003 0.35 16.45 1.66 Comparative Steel 15 tr.0.0008 0.0001 0.35 15.30 1.67 Invention Steel 16 tr. 0.0014 0.0001 0.3515..22 1.68 Invention Steel 17 tr. 0.0012 0.0002 0.35 15.17 1.69Invention Steel 18 0.0070 0.0010 0.0002 0.35 15.14 1.68 Invention Steel19 0.0240 0.0008 0.0003 0.35 15.12 1.69 Invention Steel 20 0.0420 0.00070.0001 0.35 15.09 1.69 Invention Steel 21 tr. 0.0014 0.0001 0.35 14.981.67 Invention Steel 22 tr. 0.0013 0.0003 0.35 15.07 1.67 InventionSteel 23 tr. 0.0008 0.0002 0.35 15.20 1.67 Invention Steel 24 tr. 0.00080.0002 0.35 15.70 1.67 Comparative Steel 25 tr. 0.0015 0.0003 0.35 15.591.67 Comparative Steel 26 tr. 0.0016 0.0002 0.35 14.98 1.67 InventionSteel 27 tr. 0.0017 0.0002 0.35 15.08 1.67 Invention Steel 28 tr. 0.00150.0001 0.35 15.07 1.67 Invention Steel 29 tr. 0.0013 0.0002 0.35 18.421.67 Comparative Steel 30 tr. 0.0001 0.0002 0.35 15.40 1.67 InventionSteel 31 tr. 0.0022 0.0002 0.35 15.36 1.68 Invention Steel 32 tr. 0.00280.0001 0.35 15.42 1.68 Invention Steel 33 tr. 0.0011 0.0003 0.35 15.231.67 Invention Steel 34 tr. 0.0012 0.0002 0.35 14.70 1.67 InventionSteel 35 tr. 0.0014 0.0002 0.35 14.62 1.60 Comparative Steel 36 tr.0.0013 0.0002 0.35 14.96 1.67 Invention Steel 37 tr. 0.0014 0.0001 0.3514.78 1.66 Invention Steel 38 tr. 0.0013 0.0002 0.35 15.03 1.63Comparative Steel 39 tr. 0.0013 0.0001 0.35 15.22 1.65 Invention Steel40 tr. 0.0013 0.0003 0.35 17.53 1.65 Comparative Steel 41 tr. 0.00130.0037 0.35 16.28 1.65 Comparative Steel 42 tr. 0.0014 0.0003 0.35 16.411.65 Comparative Steel 43 tr. 0.0011 0.0003 0.35 16.45 1.65 ComparativeSteel

As seen from Table 1, the steel sheets satisfying our chemicalcomposition, particularly the steel sheets decreasing Bi content areexcellent in the high-frequency iron loss property irrespective of ahigh Mn content.

1-5. (canceled)
 6. A non-oriented electrical steel sheet having achemical composition comprising C: not more than 0.005 mass %, Si: 1.5-4mass %, Mn: 1.0-5 mass %, P: not more than 0.1 mass %, S: not more than0.005 mass %, Al: not more than 3 mass %, N: not more than 0.005 mass %,Bi: not more than 0.0030 mass % and the remainder being Fe andinevitable impurities.
 7. The non-oriented electrical steel sheetaccording to claim 6, further containing one or two of Ca: 0.0005-0.005mass % and Mg: 0.0002-0.005 mass % in addition to the above chemicalcomposition.
 8. The non-oriented electrical steel sheet according toclaim 6, further containing one or two of Sb: 0.0005-0.05 mass % and Sn:0.0005-0.05 mass % in addition to the above chemical composition.
 9. Thenon-oriented electrical steel sheet according to claim 6, furthercontaining Mo: 0.0005-0.0030 mass % in addition to the above chemicalcomposition.
 10. The non-oriented electrical steel sheet according toclaim 6, further containing Ti: not more than 0.002 mass %.
 11. Thenon-oriented electrical steel sheet according to claim 7, furthercontaining one or two of Sb: 0.0005-0.05 mass % and Sn: 0.0005-0.05 mass% in addition to the above chemical composition.
 12. The non-orientedelectrical steel sheet according to claim 7, further containing Mo:0.0005-0.0030 mass % in addition to the above chemical composition. 13.The non-oriented electrical steel sheet according to claim 8, furthercontaining Mo: 0.0005-0.0030 mass % in addition to the above chemicalcomposition.
 14. The non-oriented electrical steel sheet according toclaim 11, further containing Mo: 0.0005-0.0030 mass % in addition to theabove chemical composition.
 15. The non-oriented electrical steel sheetaccording to claim 7, further containing Ti: not more than 0.002 mass %.16. The non-oriented electrical steel sheet according to claim 8,further containing Ti: not more than 0.002 mass %.
 17. The non-orientedelectrical steel sheet according to claim 11, further containing Ti: notmore than 0.002 mass %.
 18. The non-oriented electrical steel sheetaccording to claim 9, further containing Ti: not more than 0.002 mass %.19. The non-oriented electrical steel sheet according to claim 12,further containing Ti: not more than 0.002 mass %.
 20. The non-orientedelectrical steel sheet according to claim 13, further containing Ti: notmore than 0.002 mass %.
 21. The non-oriented electrical steel sheetaccording to claim 14, further containing Ti: not more than 0.002 mass%.